Remote control system by variable frequency signals



March 5, 1946.

REMOTE CONTROL SYSTEM BY VARIABLE FREQUENCY SIGNALS A. G. DE BEY 2,396,991

Filed Dec. 9, 1940 4 Sheets-Sheet 1 CROSS REFERENCE SEARCH ROOMl March 5, 1946. A. L. G. DE BEY 2,396,091

REMOTE CONTROL SYSTEM BY VARIABLE FREQUENCY SIGNALS Filed nec. 9, 1940 4 sheets-sheet 2 ffcf/ w/v ,wwf/wm 11/4 4@ ff c /P/o Hapag/cy jig 2' 4MM/H52@ 0A/D gg Mom/4mm 30 FJPfQyf/Ycyffcro/P v l 5 fr I 32 32 3/ W1# vU/ 3 /H 33 all 33' ik l nnuuunuu V QLOOOOOQQQOQQQDO Mmh 5, 1946. A L, Q DE BEY 2,396,091

REMOTE CONTROL SYSTEM BY VARIABLE FREQUENCY SIGNALS Filed Dec. 9, 1940 4 Sheets-Sheet ."5

March 5, 1946.

REMOTE CONTROL SYSTEM BY VARIABLE FREQUENCY SIGALS A. L. G. DE BEY Filed Dec. 9, 1940 4 Sheets-Sheet 4 Patented Mar. 5, 1946 REMOTE CONTROL SYSTEM BY VARIABLE FREQUENCY SIGNALS Albert Lee Gerard de Bey, West La Fayette, Ind., assignor to Purdue Research Foundation, West La Fayette, Ind., a corporation of Indiana Application December 9, 1940, Serial No. 369,216

(Cl. Z50-2) Claims.

My invention relates, generally, to remote control systems and it has particular relation to means for directing or controlling a mechanical movement or movements by means of variable frequency signals.

An object of my invention is to effect movement at a point remote from a control point in accordance with variable frequency signals transmitted from the control point to the remote point.

Another object of my invention is to translate the continuous movement of a control member at the control point into corresponding continuous movement of a controlled member at the remote point.

Still another object of my invention is to simultaneously effect different movements at the remote point in accordance with different bands of variable frequency signals transmitted from the control point.

A further object of my invention is to provide for transmitting a band of frequencies from the control point to the remote point, each frequency corresponding to a position of a movable control member at the control point, so as to operate controlled means at the remote point from any previous position corresponding to a frequency in the band to another position corresponding to another frequency therein.

A still further object of my invention is to automatically tune the receiving means at the remote point to the control frequency being received so as to thereby arrest further movement of the controlled means as long as the control frequency remains constant.

It is another object of my invention to provide for effecting operations at the remote point in addition to those performed in accordance with the variable frequency signals.

It is a further object of my invention to prevent the additional operations to be performed on receipt of the variable frequency signals.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the nature and scope of my invention reference can be had to the following detailed description, taken in connection with the accompanying drawings in which:

Figure 1 illustrates, diagrammatically, the transmitting apparatus at the control point;

Figure 2 illustrates, diagrammatically, the receiving apparatus at the remote point, such as an airplane;

' Figures 3 and 4 illustrate, diagrammatically, circuits similar to those shown in Figures 1 and 2, respectively, and in addition indicate how special operations can be performed at the remote point under the control of means at the control point; and

Figure 5 graphically illustrates certain relationships between the modulating frequencies and the plate current flow in the tubes controlled thereby.

The present invention is particularly useful in connection with controlling operation of airplanes from a control point on the ground or in another airplane. Such a control is desirable for many reasons.

When model airplanes are tested in a wind tunnel so as to permit observation of the effects of air now, it is desirable to operate the control members of the airplane as they would be operated during ight. This can be accomplished by providing controls, such as Wires, to each of the movable members and then moving them as desired. However, this has the disadvantage that it does not represent true flight conditions. By placing radio receiving apparatus on the airplane model and then providing suitable transmitting means outside of the wind tunnel, it is possible to control the various movable parts of the airplane in the wind tunnel as desired without in any way interfering with the air ow therepast.

The present invention is also useful in controlling the operation of model airplanes which are capable of making relatively short free flights. It is possible to control the altitude and direction of flight of the model airplane from a point ou the ground so as to permit the making of tests on the model under actual operating conditions.

The invention is applicable to remote control generally. It is particularly useful to operate the controls of an automotive vehicle from a stationary or from a movable remote control station. Torpedoes or moving devices that require one or more guiding operations may be guided and controlled by my invention.

According to a preferred embodiment of my invention I provide for modulating a carrier frequency with two bands of modulating frequencies which are sufficiently spaced apart so as not to overlap. The modulating frequency in each band is arranged to be continuously controlled by a single control device such as the control stick which corresponds to a similar device on an airplane. 'I'he control stick is arranged to vary the frequency in one band of modulating frequencies in accordance with movement in one plane and the frequency in the other band of modulating frequencies in accordance with movement in a plane generally at right angles to the first-mentioned plane. On the airplane, receiving circuits are provided which are individually responsive to the different bands of modulating frequencies and are incapable of responding to other frequencies. For each of these receiving means a reversible motor or its equivalent is provided, one motor being arranged to operate an elevator and the other being arranged to operate the rudder. Each of the motors is also arranged to automatically tune its receiving circuit to the modulating frequency being transmitted so that when the receiving circuit is tuned to this frequency the motor stops and remains at rest as long as this particular frequency is received. Thereby the controls of the airplane are operated by remote control underthe'control of the control stick in the same manner that they would be operated if mechanically connected to the control stick.

In a modification of the invention means are provided for transmitting from the control point one or more control frequencies outside of the band of frequencies used for controlling the twoway controlled devices on the airplane. This permits the turning oi of the ignition of the motor on the airplane and the starting of the landing gear motor or other operations that may be desired, which should be independent of the control of the elevation and direction of the airplane itself.

The continuously variable movement control system disclosed herein can be used to provide a means of remotely tuning a radio receiver to any frequency Within its tuning range Without the necessity of presetting the remote selector. A dial, duplicating that at the receiver proper, can be operated at the remote point to cause an identical movement of the tuning capacitor in the receiver. The variable frequency can be transmitted directly as a carrier over short distances and need not be superimposed on a separate carrier frequency. To provide remote volume control at the same time two separate channels can be provided or the two channels can be combined on one carrier frequency as in the case of aircraft control.

The system can be used to advantage in connection with anti-aircraft or anti-tank guns. At present a problem exists to relay data, rapidly and accurately, from a range finder position to a gun crew. Either a wired or wireless link between such stations can fbe used, adapting the variable movement control system to keep the gun automatically aimed at the target upon proper operation of the range finder by its crew.

This would eliminate delay in transmitting nre control information.

The system is also applicable to wired and especially wireless telautograph transmission. Since continuously variable movements in at least two dimensions are possible, the reproduction of combinations of movements in two dimensions at a remote point is feasible. This can be particularly applied to the rapid transmission of hand drawn maps in aerial reconnaissance from airplane to ground. The time required for transmission will fbe shorter than for various types of facsimile transmission now used.

Wireless telemetry is another application of the system disclosed herein. The reading of one electrical or other indicating instrument can be duplicated at a. remote point for each channel used in this system.

The system can be used to provide control of the rotation of rotating beam antennae such as used in television. The variable control fre,-l quency can be transmitted to the receiving unit mounted near the rotating antenna structure either by wireless or by a wired-radio system. In the latter, the low frequency variable signal can lbe transmitted on the same transmission line used to carry the high frequency television carrier, by the use of suitable isolating filters at each end of the line.

Referring now particularly to Figure 1 of the drawings, it wil .Ibe observed that the reference character I0 designates a source of carrier frequency which is connected Iby a quarter wave length transmission line, shown generally at II, across terminals I2 and I3. A low impedance twisted pair of Wires, shown generally at I4, serves to interconnect the terminals I2 and I3 and a half wave dipole antenna I5. In the work which I have done in developing the present invention, I have found that a carrier frequency of 28.9 megacycles is satisfactory. However, it will be understood that other carrier frequencies can be 'employed wi-thout departing from the scope of this invention.

For modulating the carrier frequency, a transmission line, shown generally at I6, is connected across the termina-ls I2 and I3 and has connected therein modulator tubes I'l and I8, the operation of which is controlled by oscillators I9 and 20, respectively. The oscillators I9 and 20 each constitute a source of variable control or modulating frequency which it will be understood is superimposed on the carrier frequency provided yby the source IIl thereof.

Each of the oscillators I9 and 20 is arranged to generate bands of frequency which are entirely separate and distinct from each other. For example, the oscillator I9 can be arranged to generate a band of frequency beginning at 152 kilocycles and ending at 172 kilocycles and having a mean frequency of 162 kilocycles. Likewise the oscillator 2D can be arranged to generate a band of frequencies beginning at about 182 kilocycles and ending at about 202 kilocycles with a mean frequency of 192 kilocycles. It will be observed that these bands o'f frequencies do not overlap and that there is little likelihood of interference due to harmonics.

The frequencies generated Fby the oscillators I9 and 20 are controlled 'by variable capacitors A2| and 22, respectively.

As shown, the positions of the capacitors 2I and 22 are controlled by a control stick, shown generally at 23. The control stick is arranged in a conventional manner so that its movement in one plane will effect movement of the capacitor 2|, for example, while movement in a plane at right anglesthereto will eect movement of the capacitor 22. It will be understood that the positions of the capacitors 2| and 22 will correspond to any position of the control stick in either of these two planes and that 'the movement of the control stick can take place in one plane or the other plane or in both planes simultaneously to effect corresponding movements of the capacitors 2I and 22. In turn, corresponding movement or movements of a controlled device at the remote point on an airplane, for example, are effected. It will be understood that it is unnecessary to wait for one movement to be completed before the other movement is effected. Both movements can be accomplished simultaneously.

The transmitting apparatus shown in Figure 1 wiii beviocated on the yground in a position where the controlled airplane will be visible either in a wind tunnel or during free flight. The apparatus shown in Figure 1 can also be located on another airplane which accompanies the controlled airplane during its flight.

Referring now particularly to Figure 2 of the drawings, it will be understood that the apparatus there diagrammatically illustrated is located at the remote point, such as on an airplane whose movement is to be controlled. The apparatus includes a conventional type antenna 21, similar to the antenna I5 of the transmitter which is connected to a conventional type of receiving apparatus 28 comprising a radio frequency ampliiler and modulating frequency detector as indicated. The receiving apparatus 28 is arranged to feed or energize two circuits, shown generally at 29 and 30, one circuit being individual to one band of modulating frequency and the other circuit being individual to the other band of modulating frequency. For example, the circuit 29 may be tuned to respond to the fband of modulating frequencies generated by the oscillator I9 while the circuit 39 can be arranged to respond to the band of modulating frequencies generated by the oscillator 29.

The circuit 29 comprises a circuit, shown generally at 3|, which includes a variable capacitor 32 and an inductor 33. The capacitor 32 and inductor 33 are tuned to the band of frequencies individual to the circuit 29. The inductor 33 is inductively coupled to an inductor 34 forming a part of another circuit, illustrated generally at 35. A capacitor 36 serves to capacitively interconnect the circuit 3| with the midpoint of the inductor 34. The circuit 35 includes the variable capacitor 31 which is arranged to be moved automatically, as will be hereinafter set forth, so as t0 tune the circuit 35 to the modulating frequency generated by the oscillator I9.

It will be observed that the circuit 35 is connected to plates 38 and 39 of a double diode tube, shown generally at 4D. The tube 4I) is provided with indirectly heated cathodes 42 and 43, each associated with a plate 38 and 39, respectively. It will be understood that the cathodes 42 and 43 can be individually and directly heated by batteries if desired. Resistors 44 and 45 are serially connected across the cathodes 42 and 43 and their common connection is connected, as shown, to the midpoint of the inductor 34 through an impedance 4 I.

The cathodes 42 and 43 are connected, respectively, to control electrodes 46 and 41 of control tubes shown generally at 48 and 49. A battery 50 or other suitable direct current source serves to normally apply a negative biasing voltage on the control electrodes 46 and 41, so as to maintain the tubes 48 and 49 in the non-conducting state.

The tubes 48 and 49 also include plates 52 and 53 which, as shown, are connected to the terminals of a iield winding 54 of a reversible series type motor, shown generally at 55. The motor 55 includes an armature 56 which is connected to a midpoint of the eld winding 54 and through a current source 51 to indirectly heated cathodes 58 and 59 of the tubes 48 and 49, respectively. The current source 51 can be direct current, alternating current, or interrupted direct current depending upon the type of the tubes 48 and 49, as will be readily understood.

The armature 56 of the motor 55 is connected, as shown, to move a two-way controlled device such as an elevator 60.

The armature 56 of the motor 55 is also connected, as indicated by the broken line 6|, to the capacitor 31 so that it is moved at the same time that the armature 56 is rotated. As will hereinafter appear, as long as the modulating frequency applied to the circuit 35 differs from the frequency to which it is tuned by the combination of the inductor 34 and the capacitor 31, the motor 55 will continue to operate in one direction or the other until the capacitor 31 has been moved to such position that the circuit 35 is tuned to the received modulating frequency. When this condition exists, further operation of the motor 55 ceases and it remains inoperative until the modulating frequency applied to the circuit 35 is either increased or decreased.

The sharpness of tuning of the circuits 3| and 35 is determined by the manner in which the circuit 29 is to be operated. If it is desired to vary the modulation frequency over a relatively wide range, then the circuits 3| and 35 should be correspondingly broadly tuned. If the change in modulation frequency is over a relatively narrow range, then these circuits should be more sharply tuned. The rate at which the modulation frequency is varied is also a factor. If the modulation frequency is varied at such a rate that the motor 55 cannot keep the circuit 35 tuned in step with it, then the circuits 3| and 35 should be suf.. ciently broadly tuned so that the straight line portion of the discriminator characteristic (see Figure 5) referred to the abscissa will be long enough to include the greatest frequency shift that may occur.

It will be observed that the circuit 30 is identical with the circuit 29 and, for this reason, the reference characters applied thereto are the same as applied to the circuit 29 except that they are primed. For the circuit 30, the circuits 3 I and 35' are tuned for receiving a different band of modulating frequencies, such as a band having a mean frequency of 192 kilocycles, such as generated by the oscillator 29. The motor 55' is arranged to control the operation of a two-way controlled device such as a rudder indicated at 62.

In describing the operation of the system shown in Figures 1 and 2 of the drawings, it will be assumed that initially the position of the control stick 23 is correlated with the positions of the elevator 60 and the rudder 62 so that subsequently the positions of the latter two devices can be controlled by movement of the control stick 23 to definite predetermined positions which can be marked or otherwise indicated adjacent the mounting thereof. Under these assumed conditions, the frequencies generated by the oscillators I9 and 20 are those to which the circuits 35 and 35 are tuned and, as a result, the motors 55 and 55' remain stationary. This is due to the fact that the control tubes 48, 48' and 49, 49 are maintained in the non-conducting state, thereby preventing current flow in either direction through the eld windings 54 and 54.

It will now be assumed that the control stick 23 is moved so as to effect movement of the capacitor 2| without moving the capacitor 22. It will also be assumed that the movement of the capacitor 2| is such that the frequency generated by the oscillator I9 is increased. This increased frequency is superimposed on the carrier frequency generated by the oscillator I0 and is applied to the antenna |5. The modulated frequency is received on the antenna 21, is amplified and demodulated by the receiver 28, 'I'he increased modulating frequency is applied to the circuit 29 and to the circuit 35 which is tuned to a lower frequency. Because of the 4phase differences in the voltages induced in the inductor 34 by the inductive and capacitive coupling with the circuit 3|, the resultant voltages appearing across the plate 38 and the cathode 42 on the one hand and the plate 39 and the cathode 43 on the other hand will be different. It will be assumed that the voltage across the latter will be the greater and, consequently, the voltage drop across the resistor 45 will be larger than the voltage drop across the resistor 44. This is due to the fact that the current ow indicated by the arrow 63 in the resistor 45 is greater than the current flow indicated by the arrow 64 in the resistor 44. The negative potential applied to the control electrode 41 by the battery 59 is then overcome and the tube 49 becomes conducting. Current then ows from the current source 51 through the tube 49 and the right-hand half o! the field winding 54 and the armature 56 so as to operate the latter in one direction, thereby effecting a corresponding operation of the elevator 50. At the same time, because of the mechanical connection indicated by the broken line 6I be tween the armature 56 and the capacitor 31, the latter ismoved in a direction to tune the circuit 35 to the modulating frequency being received thereby. The armature 56 continues to move until the circuit 35 is tuned to the modulating frequency. When this condition exists, the voltage drop across the resistor 45 equals the voltage drop across thel resistor 44 and the voltage applied to the control electrode 41 again becomes negative. The tube 49 then is no longer conducting and current no longer iiows through the armature 55. It then stops and remains in this psition until the modulating frequency received by the circuit 29 is changed.

If the control stick 23 has been moved to such position that the capacitor 2| decreased the frequency generated by the oscillator t9, then the current flow indicated by the arrow 64 would become greater than the current ow indicated by the arrow 53 and the tube 48 would become conducting. In this instance the lefthand half of the field winding 54 would be energized in series with the armature 56 to operate the latter in a reverse direction thereby effecting a corresponding movement of the .levator 60.

It will be understood that the motor 55' is controlled in a manner similar to that described for the motor 55 on movement of the variable capacitor 22 by the control stick 23. -It will also be understood that both of the variable'capacitors 2| and 22 can be moved at the same time thereby effecting operation of the motors 55 and 55' at the same time. Of course, if desired, individual controls could be provided for the variable capacitors 2| and 22. However, it is obviously preferable to employ single control means such as the control stick 23 so as to permit the operator at the control stick to substantially duplicate the functions of a human pilot on the air plane which is otherwise remotely controlled.

In addition to permitting. control from the ground of the direction and elevationof the airplane, it may be desirable to provide for con.- trolling additional means on the airplane. For example, it may be desirable Vto permit interruption of the ignition circuit on the airplane at the will of the operator on the ground. It may also be desirable to initiate from the ground the operation of landing gear on the airplane preparatory to its landing. It is for these Aiiufl'neses that the system shown in Figures 3 and 4 of thefdrawings can be used.

The circuit connections and apparatus shown in Figures 3 and 4 of the drawings are gen-A erally the same as shown in Figures 1 and 2 of the drawings. Accordingly, in so far as possible the same reference characters have been em- P10181 Referring first to Figure 3, it will be observed that, in addition to the variable capacitor 2| for the oscillator I9, two fixed capacitors 61 and 68 have been provided together with switches 69 and 19. The switches 69 and 10 are provided with break contact members 69a and 10a and make Contact members 69h and 10b, respectively, for controlling the connections of the capacitors 2|, 61, and 68 to the oscillator I 9.

With the switches 69 and 10 ln the positions shown in the drawings, the oscillator I9 is under the control of the capacitor 2| which in turn is operated by the control stick 23 as previously described. It will be noted that the capacitor 2| is connected to the oscillator I9 through the break contact members 69a and 10a of the switches 69 and 10. Operation of either of these switches will interrupt the circuit between the capacitor 2| and the oscillator I9. Likewise, operation of the switch 69 will connect the capacitor 61 to the oscillator I9 while operation of the switch 10 will connect the capacitor 68 thereto'. The capacitors 61 and 68 are arranged to control the operation of the oscillator I9 in such manner as to cause it to generate frequencies above or below the band of frequencies generated thereby under the control of the capacitor 2|.` Use is made of these outside frequencies, as will be indicated hereinafter, to effect the desired special control functions on the airplane.

Referring now particularly to Figure 4, it will be observed that the circuit shown generally a-t 1I thereon is similar to the circuit 29 of Figure 2. Certain additions and changes in the circuit connections have been made.

Associated with the con-trol tubes 48 and 49 are control relays shown generally at 12 and 13 having operating windings 12w and 131D and normally open contact members 12a and 13a, respectively. When the tubes 48 and 49 are rendered conducting, it will be understood that the relays 12 and 13 are respectively energized to effect corresponding operation of the motor 55 as previously described. Current for energizing the windings 12w and 13w is obtained from a suitable source such as the battery 14.

For performing the additional operations control relays shown generally at 16 and 11 are provided. These relays have operating windings 16u and 11w. The relay 1S is provided with normally open contact members 16a and 16e and normally closed contact members 1Gb. Likewise, relay 11 is provided with normally open contact members 11a and normally closed contact members 11b and 11e.

The normally closed contact members 11c can be connected in the ignition circuit of the motor which drives the airplane. The ignition circuit can be so arranged that, when the con-tact members 11c have been opened, the ignition circuit is not re-established even though the contact' members Tlc are again closed.

The normally open contact members16c can be connected in a circuit which initiates the operation of the landing gear motor. As long as they remain closed this circuit is energized. It will be understood that suitable limit switches can be employed in connection wi-th the landing gear motor so as to stop it when the landing gear has been fully extended.

An auxiliary current source such as a. battery 18 is provided for maintaining the operating windings 18w and Tlw energized after they have been initially energized.

The operating windings 'IBw and 'Hw are so arranged and constructed that they are insumciently energized to effect operation of their associated movable contact members as long as the received modulated frequency is within the band of frequencies under the control of the capacitor 2l. In order to effectively energize the operating windings 16w and 11w, it is necessary to go outside of this band of frequencies.

For a better understanding of the marginal operation o'f the relays 16 and 11, reference can be had to the curve 'I9 shown in Figure 5 of the drawings. The curve 19 represents the current flow in the plate circuits of the tubes 48 and 49 with variations in the received modulated frequency. As indicated this curve will be linear if the tubes 48 and 49 are operated as Class A amplifiers. It will be observed that variations in frequency from a mean frequency fo are plotted as abscissae and variations in plate current are plotted as ordinates, the ordinates above the axis indicating the plate current 14a for the tube 48 and the ordinates below the line indica-ting the plate current 149 for the tube 49. The capacitor 2| is arranged to control the oscillator I9 in the band of frequencies between fc and fb. At these frequencies, currents ic and ib flow through the windings 12w and TBw on the one hand and through windings 'Hw and 13w on the other hand. These currents and any currents of less value are insuflicient to energize the operating windings 'ISw and 'Hw to effect operation of their contact members.

When it is desired to operate the relay 11, the switch 6B, for example, can be operated. When this is done, the capacitor 2| is disconnected from the oscillator I9 and the capacitor 61 is connected thereto. The capacitance of the capacitor 61 is such that the generator I9 is caused to generate a frequency outside of the band of frequencies generated thereby under the control of the capacitor 2| and this frequency can be represented as the frequency fd on Figure 5. As a result, an increased current id flows in the plate circuit of the tube 49 which is sufl'lcient to effect the movement of the contact members of the relay 11 to their alternate positions.

Contact members 11o are then opened to open the ignition circuit as previously described. A holding circuit for the relay 11 is then completed at contact members 11a through normally closed contact members 16h of relay 16 to the battery 18. It is then unnecessary to hold the switch 69 in the operated position and maintain the frequency fd any longer than is necessary to operate the relay '11 to the closed position.

The time required to effect the operation of the relay 11 as previously described is extremely small and consequently, even though the relay 13 will be energized at the same time, it will be promptly de-energized as soon as the switch E9 is released. Consequently, because of the inertia of the motor 55 and the apparatus connected therewith, it will not bc energized for a time sufciently long to permit it to change its position.

The relay 11 can be deenergized and the relay 16 energized by operating the switchflil. When the switch 10 is operated, the capacitor 2| is disconnected from the oscillator I9 and the capacitor 68 is connected thereto. The capacitor 68 is arranged to cause the oscillator I9 to generate a frequency, such as the frequency fa which is lower than any frequency generated by the oscillator I9 under the control of capacitor 2l. A current ia then ows in the plate circuit of the tube 48 which is sufficient to eifect operation of the relay 16.

At contact members 15e a circuit is completed, as previously indicated, for starting the operation of the landing gear motor. At contact members 16o the holding circuit for the relay 11 is opened and it is deenergized. At contact members 16a a holding circuit for the relay 16 is partially completed which is fully completed on closure of contact members 11b.

It will be understood that the relay 16 can be deenergized by again operating the switch 69 to again eiect the operation of the relay 11.

Since certain further changes can be made in the foregoing constructions and circuit arrangements and different embodiments of the invention can be made without departing from the scope thereof, it is intended that all matter shown in the accompanying drawings and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. Apparatus for remotely controlling an airplane or the like from a control point on the ground or in another airplane comprising, in combination, means at the control point for transmitting a carrier frequency, means for simultaneously modulating the carrier frequency with a plurality of independently variable frequencies, means for varying each frequency in accordance with individually desired movements on the\ remotely controlled airplane, means on the controlled airplane for receiving the modulated carrier frequency, a plurality of means on the controlled airplane each individually movable in opposite directions in synchronism with increase or decrease of the received individual modulating frequency-from a previous value to effect said desired movements, and means individual to each of the last named means and operable in accordance with the movement thereof for tuning the modulating frequency receiving means individual thereto to the modulating frequency received thereby.

2. Apparatus for remotely controlling an airplane or the like from a control point on the ground or in another airplane comprising, in combination, means at the control point for transmitting a carrier frequency, means for simultaneously modulating the carrier frequency with a plurality of different bands of frequencies, means for continuously varying the modulating frequency in each band of frequencies in accordance with a plurality of different movements of a control stick or the like from one position to another each movement corresponding to desired change in position of one of a plurality of controlled means on the controlled airplane, means on the controlled airplane for receiving the modulated carrier frequency, a plurality of means -en the controlled airplane each continuously movable in opposite directions individually in respense to its one of the received modulating frequencies for operating the controlled means individual thereto in synchronism with increase or decrease of its modulating frequencyfrom a previous value in its band of frequencies, and means operable in accordance with the movement of each controlled means for tuning its modulating frequency receiving means to the received modulating frequency whereby each controlled means remains in any position to which it has been operated as long as the modulating frequency individual thereto remains constant.

3. Apparatus for remotely controlling an .tirplane or the like from a control point on the ground or in another airplane comprising, in combination. means at the control point for transmitting a carrier frequency, means for simultaneously modulating the carrier frequency with a plurality of different bands of frequencies, variable impedance means for continuously varying the modulating frequency in each band of frequencies in accordance with a plurality of different movements of a control stick or the like from one position to another each movement corresponding to desired change in position of one of a plurality of controlled means on the controlled airplane, means on the controlled airplane for receiving the modulated carrier frequency, a reversible motor for each controlled means for operating the same, a plurality of circuit means each individually energized from said receiving means and tuned to be responsive only to the band of modulating frequencies individual thereto, variable impedance means for tuning each circuit means to any particular frequency in its band of frequencies, means controlled by each circuit means for operating one of said motors in one direction in synchronism with increase in the modulating frequency in its band above said particular frequency and in the opposite direction in synchronism with decrease in the modulating frequency below said particular frequency, and means operatively interconnecting each motor and the variable impedance means individual thereto for tuning its circuit means to the modulating frequency being received thereby whereby each controlled means remains in any position to which it has been operated as long as the modulating frequency individual thereto remains constant.

4. Apparatus for remotely controlling an airplane or the like from a control point on the ground or in another airplane comprising. in combination. means at the control point for transmitting a carrier frequency, means for modulating the carrier frequency with a variable frequency, means for varying the modulating frequency Within predetermined limits in accordance with a desired movement on the remotely controlled airplane, means for modulating the carrier frequency with a frequency outside of said limits, means on the controlled airplane for receiving the modulated carrier frequency. means on the controlled airplane movable in opposite directions, means on the airplane responsive to increase or decrease of the received modulating frequency, means operatively interconnecting said frequency responsive means and said means movable in opposite directions so as to move the same in synchronisn; with increase or decrease 0f the received modulating frequency from a previous value to effect said desired movement, and operating means on the controlled airplane incapable of responding to any received modulating frequency within said limits but capable of responding on receipt of said modulating frequency outside of said limits.

5. Apparatus for remotely controlling an airplane or the like from a control point on the sround or in another airplane comprising, in

combination, means at the control point for transmitting a carrier frequency, means for modulating the carrier frequency with a variable frequency, means for varying the modulating frequency within predetermined limits in accordance with a desired movement on the remotely controlled airplane, means for modulating the carrier frequency with a frequency outside of said limits. control means for the last named means when operated being effective to discontinue the application of the modulating frequency within sa'd limits so as to modulate said carrier frequency only with said frequency outside of said limits. means on the controlled airplane for receiving the modulated carrier frequency, means on the controlled airplane movable in opposite directions in accordance with increase or decrease of the received modulating frequency from a previous value to effect said desired movement. means operable in accordance with the movementl of said movable means for tuning the modulating frequency receiving means to the received modulating frequency. and operating means on the controlled airplane incapable of responding to any received modulating frequency within said limits but capable of responding on receipt of said modulating frequency outside of said limits on operation of said control means.

6. Apparatus for remotely controlling an airplane cr the like from a control point on the ground or in another airplane comprising. in combination, means at the control point for transmitting a carrier frequency, means for modulating the carrier frequency with a band of frequencies, means for continuously varying the modulating frequency in said band of frequencies in accordance with the movement of a control stick or the like from one position to another corresponding to desired change in position of controlled means on the controlled airplane. means for modulating the carrier frequency with a frequency outside of said limits` control means for the last named means when operated being effective to discontinue the application of the modulating frequency in said band of frequencies so as to modulate said carrier frequency only with said frequency outside of said limits, means on the controlled airplane for receiving the modulated carrier frequency, means responsive to the received modulating frequency for operating .said controlled means in opposite directions continuously in accordance with increase or decrease of the received modulating frequency from a previous value in said band of frequencies, and operating means on the controlled airplane incapable of responding to any received modulating frequency within said band of frequencies but capable of responding on receipt of said modulating frequency outside of said band of frequencies on operation of said control means. u

'7. Apparatus for remotely controlling an airplane or the like from a. control pointbn the ground or in another airplane comprising, in combination, means at the control point for transmitting a carrier frequency, means for modulating the carrier frequency with a band of frequencies, variable impedance means for continuously varying the modulating frequency in said band of frequencies in accordance with the movement of a control stick or the like from one position to another corresponding to desired change in position of controlled means on the controlled airplane, xed impedance means for modulating the carrier frequencies, control means for said fixed impedance means when operated being effective to disconnect said variable impedance means and discontinue the application of the modulating frequency in said band of frequencies so as to modulate said carrier frequency only with said frequency outside of said band of frequencies, means on the controlled airplane for receiving the modulated carrier frequency, reversible motor means for operating said controlled means in opposite directions, means responsive to change in the received modulating frequency for operating said motor means in opposite directions continuously in accordance with increase or decrease of the received modulating frequency from a previous value in said band of frequencies, variable impedance means operable in accordance with the movement of said motor means for tuning the modulating frequency receiving means to the particular modulating frequency being received whereby said motor means is deenergized and remains in the position corresponding to said particular frequency as long as the modulating frequency remains constant, and operating means on the controlled airplane incapable of responding to any received modulating frequency within said band of frequencies but capable of responding on receipt of said modulating frequency outside of said band of frequencies on operation of said control means.

8. Apparatus for remotely controlling an airplane or the like from a control point on the ground or in another airplane comprising, in combination, means at the control point for transmitting a carrier frequency, means for modulating the carrier frequency with a variable frequency,

means for varying the modulating frequencyV within predetermined limits in accordance with a desired movement on the remotely controlled airplane, means for modulating the carrier frequency with two frequencies one above and the other below the frequencies within said limits, means on the controlled airplane for receiving the modulated carrier frequency, means on the controlled airplane movable in opposite directions in accordance with increase or decrease of the received modulating frequency from a previous value to effect said desired movement, and two operating means on the controlled airplane each incapable of responding to any received modulating frequency within said limits but one being capable of responding on receipt of one of said is;

modulating frequencies outside of said limits and the other being capable of responding to the other of said modulating frequencies outside of said limits.

9. Remote control apparatus comprising, in

- connection between combination, means for receiving a variable control frequency including a tunable circuit having a variable impedance device, a resistor, means interconnecting said tunable circuit and said resistor whereby current flow through the latter is controlled according to the degree that said tunable circuit is out of tune with the received frequency, and a pair of electric valves each having an anode, a cathode and a control electrode, said cathodes of said valves being interconnected and said control electrodes being connected to said resistor so that the conductivity of said valves is controlled in accordance with the magnitude and direction of current ow therethrough; a. reversible electric motor interconnected between said anodes of said valves and the connection between said cathodes thereof through a current source and adapted to rotate in one direction or the other depending upon which of said valves is conducting, and means operatively interconnecting said motor and said variable impedance device for moving the latter to tune said circuit to the frequency applied thereto, whereupon said valves are rendered noncondueting and said motor is deenergized.

10. Remote control apparatus comprising, in combination, means at a control point for transmitting a variable frequency to a remote point; means at the remote point for receiving the transmitted frequency including a tunable circuit having a variable impedance device, a resistor, means interconnecting said tunable circuit and said resistor whereby current ow through the latter is controlled according to the degree that said tunable circuit is out of tune with the received frequency, and a pair of electric valves each having an anode, a cathode and a control electrode, said cathodes 0f said valves being interconnected and said control electrodes being connected to said resistor so that the conductivity of said valves is controlled in accordance with the magnitude and direction of current flow therethrough; a reversible electric motor interconnected between said anodes of said valves and the said cathodes thereof through a current source and adapted to rotate in one direction or the other depending upon which of said valves is conducting, and means operatively interconnecting said motor and said variable impedance device for moving the latter to tune said circuit to the frequency applied thereto, whereupon said valves are rendered non-conducting and said motor is deenergized.

ALBERT LEE GERARD DE BEY. 

